1. Field of the Invention
The present invention relates to a power supply device that includes a contactor which connects a power supply and a load and a method for making a decision as to weld of the contactor.
2. Description of Related Art
In a power supply device for a hybrid vehicle and the like, which converts output from a direct current power supply into alternate current through an inverter so as to drive an AC motor, a secondary battery is used as a DC power supply. A positive contactor is connected in series between positive electrodes of the secondary battery and the inverter, and a negative contactor is connected in series between negative electrodes of the secondary battery and the inverter. In addition, a precharge contactor is connected in parallel with the positive contactor through a resistor.
A capacitor for smoothing DC voltage is provided between the positive electrode and the negative electrode on the inverter side. Electrical power supply from the secondary battery to the inverter is carried out by at first setting the precharge contactor and the negative contactor to a closed state so that the inverter initially charges the capacitor, and, after holding the capacitor voltage close to that at the secondary battery, setting the positive contactor to a closed state.
There is a widely used technique in which a capacitor is thus charged so as to keep the inrush current low when the positive contactor is set to the closed state and prevent contact welding at the contactor. However, a contactor may be welded at a contact due to an arc struck in the contact upon an open/close operation or due to aging, and, if the contactors of both of the positive electrode and the negative electrode are welded, the secondary battery and the inverter can not be separated. Hence, a technique to make a decision as to contactor weld and processing to inhibit a close operation at the contactor when weld is detected are necessary.
For example, there is a technique for making a decision as to contactor weld such as that described in Japanese Laid-Open Patent Publication No. 2000-134707. In the technique, at the start of electrical power supply from a secondary battery, i.e., a DC power supply, to load, only a precharge contactor is set to a closed state initially, so that a decision is made as to weld of a negative contactor based upon the capacitor voltage at the time. If the negative contactor is welded, the capacitor voltage rises by just setting the precharge contactor to the closed state, and hence a decision can be made as to weld.
Following this, after the negative contactor is also set to the closed state so as to charge the capacitor to a predetermined voltage level, a decision is made as to weld of the positive contactor or the precharge contactor based upon the capacitor voltage when the precharge contactor is set to the open state. If the positive contactor or the precharge contactor is welded, the capacitor voltage does not drop, and hence a decision can be made as to weld.
However, the above conventional technique requires an open/close operation of the contactor for making a decision as to weld and requires charging the capacitor to the predetermined voltage level, and therefore it takes time before the decision-making is completed. While the negative contactor is set to the closed state so as to make a decision as to weld of the positive contactor and weld of the precharge contactor, the negative contactor may also have been welded by excessive current flowing thereinto due to the difference between the uncharged capacitor voltage and DC power supply voltage if the positive contactor is welded.
For this reason, in Japanese Laid-Open Patent Publication No. 2007-295699, at the start of electrical power supply from the DC power supply to the load, voltage of a power supply for accessories is boosted by a boost circuit, and the positive contactor or the negative contactor is set to the closed state with the capacitor voltage raised to the extent of the DC power supply voltage due to the boost, so that a decision is made as to weld of the negative contactor or the positive contactor based upon the change in the capacitor voltage at the time. The capacitor is fully charged when the positive contactor or the negative contactor is set to the closed state. Therefore, even if one of the contactors is welded, no excessive current is generated at the contactor set to the closed state.
However, that method requires the boost circuit for charging the capacitor voltage to the extent of the DC power supply voltage. In addition, since after the capacitor voltage is charged to the extent of the DC power supply voltage, the close operation of the contactor is performed and weld decision-making is carried out, it took time before the decision-making is completed.